Esters have been used as lubricating oils for over 50 years. They are used in a variety of applications ranging from jet engines to refrigeration. In fact, esters were the first synthetic crankcase motor oils in automotive applications. However, esters gave way to polyalphaolefins (PAOs) due to the lower cost of PAOs and their formulation similarities to mineral oils. In full synthetic motor oils, however, esters are almost always used in combination with PAOs to balance the effect on seals, additives solubility, volatility reduction, and energy efficiency improvement by enhanced lubricity.
Ester-based lubricants, in general, have excellent lubrication properties due to the polarity of the ester molecules of which they are comprised. The polar ester groups of such molecules adhere to positively-charged metal surfaces creating protective films which slow down the wear and tear of the metal surfaces. Such lubricants are less volatile than the traditional lubricants and tend to have much higher flash points and much lower vapor pressures. Ester-based lubricants are excellent solvents and dispersants, and can readily solvate and disperse the degradation by-products of oils. Therefore, they greatly reduce sludge buildup. While ester-based lubricants are stable to thermal and oxidative processes, the ester functionalities give microbes a handle to do their biodegrading more efficiently and more effectively than their mineral oil-based analogues. However, the preparation of esters is more involved and more costly than the preparation of their PAO counterparts.
Diester-based lubricants and their manufacture have been recently reported, wherein the diester species have a general formula:
where R′1, R′2, R′3, and R′4 are the same or independently selected from a C2 to C17 carbon fragment. See commonly-assigned U.S. patent application Ser. Nos. 11/673,879 (Miller et al.), filed Feb. 12, 2007 and published as United States Patent Publication No. US 20080194444 on Aug. 14, 2008; and Ser. No. 12/023,695 (Miller et al.), filed Jan. 31, 2008. Note that the two ester groups are vicinal in their attachment to the aliphatic backbone of the diester species.
In view of the foregoing, and not withstanding such above-described advances in diester-based lubricant synthesis, facile methods of generating diester-based lubricants would be extremely useful—particularly wherein the diester species in said lubricants can deviate from the vicinal arrangement of the esters groups in relation to their aliphatic backbone.